This application requests funds to purchase the MR Solutions MRS-3031/PET-SIM-2R-PLUS PET/MR animal imaging scanner. The instrument is a small animal scanner combining the imaging capabilities of high-resolution, high sensitivity of Positron Emission Tomography (PET) and high-contrast anatomical Magnetic Resonance Imaging (MRI) in the same gantry. The combination of features within the MR Solutions PET/MR is optimal for supporting our diverse research portfolios at Washington University by providing high-resolution PET imaging for improved quantitation accuracy in small objects and exquisite anatomical images provided by high contrast MR images that are intrinsically registered to PET. Anatomical registration to functional images is now a prerequisite for the development of PET probes targeting the study of diseases using animal models in fields such as oncology, neurology, cardiology, immunology and pulmonary sciences. The Mallinckrodt Institute of Radiology is involved in numerous research projects, in the vast part supported by NIH grants, by the implication of a wide array of researchers. This camera will allow the developments of imaging agents and to study the physiology and anatomy in animal models of human diseases in vivo. The MR Solutions PET/MR will fulfill the long-term objective to perform combined PET/MR imaging in small animal models and thus will support the ongoing and future research growth at Washington University.